This invention relates to a polishing pad used for polishing the surface of a workpiece made of a material such as metals, glass and crystals and more particularly a workpiece with a surface requiring a high level of flatness such as a semiconductor wafer, a semiconductor device wafer, a liquid crystal display element, a thin-film audio-visual device, a magnetic disk substrate, an optical disk substrate and a crystal substrate such as a quartz substrate, as well as a method of its production and a method of polishing.
Semiconductor devices and magnetic disks are used as main components of electronic apparatus such as telephones, cameras and computers for controlling functions and storing and displaying data. The surface of a workpiece such as a semiconductor device wafer used in such an electronic component undergoes various processes required for the production of various electronic components such as a multi-layer wiring process and a film deposition process as well as an inspection process before such component is presented as a finished product. Such series of processes for the production of such workpieces must be carried with the accuracy level in units of nanometers such that the component characteristics and functions expected at the design stage can be fully realized. This means that each of the processes must be carried out at a very high level of accuracy, and the polishing process, for example, is required to flatten the surface of the workpiece evenly to a very high degree.
The surface polishing process on a workpiece, of which such a high level of accuracy is required, is carried out by rotating a lapping plate with a polishing pad adhered onto its surface, supplying a slurry with abrading particles dispersed therein, and pressing the workpiece thereonto while the lapping plate is continuously rotated. In such a polishing process, it has been a common practice to use a cloth pad of a woven or non-woven cloth material or a foamed pad as the polishing pad. It was because such polishing pads are soft and flexible and hence capable of following the contour of the surface of the workpiece and have gaps and air bubble voids on its surface capable of taking polishing debris thereinto and hence were believed capable of flatten the surface of the workpiece to a highly accurate level, as disclosed in Japanese Patent Publications Tokkai 2000-239651 and 2005-88174.
In a multi-layer wiring process or a film deposition process, such as mentioned above, however, if a next layer is formed over an underlying layer with an uneven surface, the upper surface of the subsequently formed upper layer (such as the surface of a multi-layer structure of a semiconductor device wafer) becomes uneven similarly to the uneven surface of the underlying layer therebelow. If this surface of the upper layer thus formed is polished by using a polishing pad which is soft and flexible as described above, a gentle unevenness is formed on the surface, caused by this uneven upper surface, and the surface of the workpiece cannot be flattened to a desired high level of accuracy.
For this reason, fixed-particle polishing pads which have abrading particle dispersed and affixed inside and on the surface of a resin sheet or a resin plate and are harder than the polishing pads described above (and hence less elastic and less capable of following the contour of the target surface to be polished) have been proposed, as described in Japanese Patent Publications Tokkai 2005-7520 and 2005-129644.
In the technical field of polishing a workpiece requiring a highly evenly flattened surface, on the other hand, a new technology is always in demand for flattening the surface of a workpiece quickly (that is, with a higher polishing rate) and less expensively without forming any scratches. In recent years, in particular, a technology is being required for flattening at a reduced cost and at a polishing rate of 2000 Å/minute or more without forming scratches.
In general, if abrading particles of a large size are applied to the surface of a workpiece, they have an effect of flattening the surface at an increased polishing rate. Since larger abrading particles tend to form unwanted scratched on the surface, however, it becomes difficult to obtain a flattened surface without scratches. If abrading particles of a smaller size are applied to the surface, on the other hand, they have the advantage of being able to flatten the surface without forming scratches but it is well known by persons skilled in the art that the polishing rate becomes low and the flattening process becomes inconveniently time-consuming.
In view of the above, it has been known (as described in aforementioned Japanese Patent Publication Tokkai 2005-129644) to use abrading particles of a larger size by dispersing and securely affixing them within and on the surface of a resin sheet such that the abrading particles will not fall off and the formation of scratches by such fallen particles can be reduced. It has also been known (as described in aforementioned Japanese Patent Publication Tokkai 2005-7520) to use abrading particles of a smaller size by dispersing and affixing them within and on the surface of a resin sheet such that the hardness of the polishing pad itself is adjusted, or using a polishing liquid obtained by adding a reaction liquid capable of chemically reacting with the surface of the workpiece or a polishing slurry having abrading particles dispersed therein together with the fixed-particle polishing pad.
Although abrading particles of a larger size are securely affixed to a resin sheet as described above according to a prior art technology such that small particles will not fall off, this has only the effect of reducing the scratches. Since the size of the abrading particles acting on the surface of the workpiece is large, there still remains the problem that the surface cannot be flattened to a high level of accuracy. If a reaction liquid or a polishing slurry is used, furthermore, it becomes costly not only in expense and in time for the material and preparation but also for the processing of the waste liquid generated during the polishing process. Although a polishing liquid with a reaction liquid added thereto is used in combination with a fixed-particle polishing pad, a high polishing rate cannot be obtained. (The polishing rate as described in aforementioned Japanese Patent Publication Tokkai 2005-7520 is 800 Å/minute).